The production of shaped synthetic members from synthetic granulated particles, which was superficially plasticised, then compressed under pressure to form a preform, which is then extruded in turn into a moulding cavity, has become known by the name "impact sintering". This method is therefore advantageous because one the one hand the consumption of energy is relatively low (in this method the mass of synthetic material remains unsintered) and on the other hand because thick-walled shaped synthetic members can be produced without shrinkage, which cannot be produced with normal casting processes.
The superficial plasticisation of the synthetic granulated particles, which is a pre-requisite in "impact sintering", can be brought about in various ways. Thus the synthetic granulated particles can be softened superficially by a solvent; as an alternative, a selective heating of the (blackened) surfaces of the granulated particles by microwaves in a resonator is considered. A further known possibility for the surface plasticisation, with which the present invention deals, consists of producing a mixture of the synthetic granulated particles and a conducting powder and then of passing an electric current through this mixture. This current flows through the conducting powder, which clings to the surface of the granulated particles and sinters the surface of the granulated particles in the desired manner in the case of corresponding control of the method.
In the known method, pure conducting powder in the form of graphite particles ("conducting carbon black") is added to the synthetic granulated material. In this case there is a great danger that the pure graphite particles may become heated excessively in the flow of current so that the synthetic material decomposes and no sintering occurs. The conducting powder forms a cohesive layer between the individual granulated particles and thus prevents their intimate bonding.